A fine bayonet,
Species & Appearance ref. -- Bayonets are swords, traditionally silver in color. Faelene has a silver horn.
Strung by brigands,
History ref. -- Brigands are robbers, and Faelene was taken from the Basin and is held captive by Kri.
Made abrasive by grit,
Can make a chilling weapon.
Herd ref. -- Faelene is officially a member of the Basin, which is CHILLY.
Perhaps during the masque,
You would kindly stab brutes in the back?
Could be a reference to the thread she is in with Kri currently, called "a knife in my back".